Method and apparatus for processing a substrate

Abstract

Methods and apparatuses for processing a substrate are provided herein. For example, a magnet-to-target spacing system configured for use with an apparatus for processing a substrate includes a sensor configured to provide a signal corresponding to a distance between a front face of a magnet and a back face of a target while rotating the magnet relative to the target, and a magnet controller configured to control the distance between the front face of the magnet and the back face of the target based on the signal provided by the sensor.

Description

Technical Field

[0001] The embodiments of this disclosure generally relate to methods and apparatus for processing substrates. More specifically, embodiments of this disclosure relate to automatically increasing or decreasing the distance between a magnet and a target (MT) using a sensor feedback system. Background Technology

[0002] Conventional plasma processing (physical vapor deposition) chambers use one or more magnets to facilitate the guidance of sputtered material plasma toward a substrate. For example, a magnetron assembly may be positioned above a target disposed within a processing volume of the processing chamber. The magnetron may include multiple magnets configured to generate a magnetic field within the processing chamber near the front of the target to produce plasma, thus causing a significant ion flux to bombard the target, resulting in the sputtering of target material toward the substrate.

[0003] The plurality of magnets may be spaced apart from the back side of the backplate to which the target is attached. The spacing between the plurality of magnets and the target is a critical parameter that can significantly affect the specifications of the film deposited on the substrate. For example, the spacing between the plurality of magnets and the target can affect the film deposition rate, the film deposition profile (e.g., inconsistent thickness across the substrate), and can lead to target bending (which can result in inconsistent spacing, increased DC voltage at the target radius, and can deteriorate during the target lifetime), backplate scratches, etc. Summary of the Invention

[0004] This document provides methods and apparatus for processing substrates. In some embodiments,

[0005] For example, a magnet-to-target spacing system configured for use with a device for processing a substrate includes: a sensor configured to provide a signal corresponding to the distance between the front side of the magnet and the back side of the target while rotating the magnet relative to the target; and a magnet controller configured to control the distance between the front side of the magnet and the back side of the target based on the signal provided by the sensor.

[0006] According to at least some embodiments, a processing chamber for processing a substrate includes: a substrate support disposed within a processing volume of the processing chamber and configured to support the substrate; a target configured to sputter material toward the substrate support; a magnetron including a magnet rotatable along a path during operation; a sensor configured to provide a signal corresponding to the distance between the front side of the magnet and the back side of the target while the magnet is rotated relative to the target; and a magnet controller configured to control the distance between the front side of the magnet and the back side of the target based on the signal provided by the sensor.

[0007] According to at least some embodiments, a method for processing a substrate includes detecting the distance between the front side of the magnet and the back side of the target while rotating a magnet relative to a target; and controlling the distance between the front side of the magnet and the back side of the target to a desired value based on the detected distance.

[0008] Other and further embodiments of this disclosure are described below. Attached Figure Description

[0009] The embodiments of this disclosure, which have been briefly summarized above and are discussed in more detail below, can be understood by referring to the illustrative embodiments depicted in the accompanying drawings. However, the drawings illustrate only typical embodiments of this disclosure and should not be considered as limiting the scope, as this disclosure may allow for other equally effective embodiments.

[0010] Figure 1 This is a schematic cross-sectional view of a processing chamber according to at least some embodiments of the present disclosure.

[0011] Figure 2 It is configured for use with at least some embodiments of this disclosure. Figure 1 A diagram of a magnet-to-target spacing system used in the processing chamber.

[0012] Figure 3 It is configured for use with at least some embodiments of this disclosure. Figure 1 A diagram of a magnet-to-target spacing system used in the processing chamber.

[0013] Figure 4 This is a flowchart of a method for processing a substrate according to at least some embodiments of the present disclosure.

[0014] To facilitate understanding, the same reference numerals are used to denote shared elements in the figures where possible. The figures are not drawn to scale and may be simplified for clarity. Elements and features of one embodiment may be advantageously incorporated into other embodiments without further description. Detailed Implementation

[0015] This document provides embodiments of methods and apparatus for processing substrates. For example, the methods and apparatus described herein provide an improved way to maintain optimal spacing between one or more magnets of a magnetron and the target throughout the target's lifetime. For instance, the magnet-to-target spacing system includes a sensor configured to provide a signal corresponding to the distance between the front face of the magnet and the back face of the target while the magnet is rotated relative to the target. The magnet-to-target spacing system also includes a magnet controller configured to control the distance between the front face of the magnet and the back face of the target based on the signal provided by the sensor. The methods and apparatus described herein provide a direct and simple solution to maintain an appropriate spacing between one or more magnets and the target, which in turn minimizes (if not eliminated) the effects of target curvature. The movement of one or more magnets can be automatic and requires no external intervention. Furthermore, the methods and apparatus described herein provide automatic adjustment of the MT spacing, applicable to different processing chambers requiring stable MT spacing to maintain good film properties, capable of operating / controlling processing chambers with target curvature and maintaining film properties, capable of solving coverage problems associated with MT spacing, and providing low manufacturing costs because only a laser sensor is added to existing hardware, and is not limited to the target material.

[0016] Figure 1 A schematic side view of a processing chamber 100 (e.g., a plasma processing chamber) according to at least some embodiments of the present disclosure is depicted. In some embodiments, the processing chamber 100 is a PVD processing chamber adapted to sputter deposited material on a substrate having a given diameter. Illustrative examples of suitable PVD chambers that may benefit from the present disclosure include those available from Applied Materials, Inc., of Santa Clara, California. Other processing chambers available from Applied Materials and other manufacturers may also be modified according to the embodiments described herein.

[0017] The processing chamber 100 typically includes an upper sidewall 102, a lower sidewall 103, a grounding adapter 104, and a cover assembly 111, which define a body 105 that encloses the internal volume 106. An adapter plate 107 may be disposed between the upper sidewall 102 and the lower sidewall 103.

[0018] A substrate support 108 is disposed within the internal volume 106 of the processing chamber 100. The substrate support 108 is configured to support a substrate having a given diameter (e.g., 150 mm, 200 mm, 300 mm, 450 mm, etc.). A substrate transfer port 109 is formed in the lower sidewall 103 for transferring the substrate into and out of the internal volume 106.

[0019] Gas source 110 is coupled to processing chamber 100 to supply processing gas to internal volume 106. Process gases may include, if desired, inert, non-reactive, and reactive gases. Examples of process gases that may be supplied by gas source 110 include, but are not limited to, argon (Ar), helium (He), neon (Ne), nitrogen (N2), oxygen (O2), water (H2O) vapor, and other rare gases.

[0020] Pumping device 112 is coupled to processing chamber 100, which communicates with internal volume 106, to control the pressure in internal volume 106. In at least some embodiments, the pressure level in processing chamber 100 can be maintained from about 1 millitor to about 1 tor during deposition, for example, from about 300 millitor to about 500 millitor.

[0021] Grounding adapter 104 may support a target, such as target 114. Target 114 is made of a material to be deposited on a substrate. In at least some embodiments, target 114 may be made of aluminum (Al), cobalt (Co), copper (Cu), nickel (Ni), tantalum (Ta), titanium (Ti), tungsten (W), alloys thereof, combinations thereof, etc. In at least some embodiments, processing chamber 100 is configured to deposit, for example, aluminum oxide (AlO2), aluminum oxynitride (such as AlON), Co, Cu, Ta, tantalum nitride (TaN), tantalum oxynitride (TaO) on the substrate. x N y Ti, titanium oxynitride (TiO) x N y ), W, or tungsten nitride (WN).

[0022] Target 114 may be coupled to a source component including a power supply 117 for target 114. For example, power supply 117 may be an RF power supply, which may be coupled to target 114 via a matching network 116. In some embodiments, power supply 117 may alternatively be a DC power supply, in which case the matching network 116 is omitted. In some embodiments, power supply 117 may include both a DC power source and an RF power source. Furthermore, in some embodiments, target 114 may include a backplane (…). Figure 1 (Not shown in the image), the backplate may be provided to improve the structural stability of the target 114. The backplate may contain a conductive material, such as copper-zinc, copper-chromium, or the same material as the target 114, such that RF and optional DC power can be coupled to the target 114 via the backplate. Alternatively, the backplate may be non-conductive and may include conductive elements (not shown), such as electrical penetrations.

[0023] A magnetron 170 is positioned above a target 114 and may include one or more magnets 172 rotatable along a path, supported by a base plate 174 connected to an axis 176 axially aligned with the central axis of the processing chamber 100 and the substrate 101. The one or more magnets 172 generate a magnetic field within the processing chamber 100 near the front of the target 114 to generate plasma 165, resulting in a significant ion flux impacting the target 114 and causing sputtering emission of target material. The one or more magnets 172 may rotate about the axis 176 to increase the uniformity of the magnetic field across the surface of the target 114. Typically, the one or more magnets 172 may be rotated such that during rotation, the innermost magnet position is positioned above or outside the diameter of the substrate being processed (e.g., the distance from the axis of rotation to the innermost position of the one or more magnets 172 is equal to or greater than the diameter of the substrate being processed).

[0024] Collimator 118 may be positioned within an internal volume 106 between target 114 and substrate support 108. The central region 135 of collimator 118 typically corresponds to the diameter of the substrate being processed (e.g., equal to or substantially equal to the diameter of the substrate). Therefore, the peripheral region 133 of collimator 118 typically corresponds to an annular region radially outward of the substrate being processed (e.g., the inner diameter of peripheral region 133 is substantially equal to or greater than the diameter of the substrate). In some embodiments, collimator 118 may be electrically biased to control the ion flux to the substrate and the neutral angle distribution at the substrate, and to increase the deposition rate due to the increased DC bias.

[0025] Collimator 118 is coupled to upper shield 113, which in turn is coupled to processing tool adapter 138. Processing tool adapter 138 may be made of a suitable conductive material compatible with the processing conditions in processing chamber 100. Insulating rings 156 and 157 are disposed on either side of processing tool adapter 138 to electrically insulate processing tool adapter 138 from ground adapter 104. Insulating rings 156 and 157 may be made of a suitable processing-compatible dielectric material.

[0026] In at least some embodiments, a first set of magnets 196 may be positioned adjacent to a grounding adapter 104 to help generate a magnetic field that guides ions expelled from the target 114 through a peripheral region 133. In at least some embodiments, a second set of magnets 194 may be positioned to form a magnetic field between the bottom of the collimator 118 and the substrate, thereby guiding metal ions expelled from the target 114 and distributing the ions more evenly over the substrate 101. In at least some embodiments, a third set of magnets 154 may be positioned between the first set of magnets 196 and the second set of magnets 194, and generally centered on or below the substrate-facing surface of the central region 135 of the collimator 118, to further guide metal ions toward the center of the substrate 101.

[0027] The processing tool adapter 138 includes one or more features to facilitate support for processing tools, such as collimator 118, within the internal volume 106. For example, such as... Figure 1 As shown, the processing tool adapter 138 includes a mounting ring or bracket 164 that extends radially inward to support the upper shield 113.

[0028] In some embodiments, a coolant passage 166 may be provided in the processing tool adapter 138 to facilitate coolant flow through the processing tool adapter 138, thereby removing heat generated during processing. For example, the coolant passage 166 may be coupled to a cooling device 153 (coolant source) to provide a suitable coolant, such as water (deionized water), nitrogen, argon or other rare gases, clean dry air (CDA), or corrosive gases. The coolant passage 166 advantageously removes heat from the processing tool (e.g., collimator 118) that is not easily transferred to other cooling chamber components (such as grounding adapter 104).

[0029] A radially inwardly extending flange (e.g., a mounting ring or bracket 164) is provided to support an upper shield 113 within a central opening in the internal volume 106 of the processing chamber 100. The bracket 164 may be positioned near the coolant passage 166 to facilitate maximizing heat transfer of the coolant flowing from the collimator 118 to the coolant passage 166 during use.

[0030] A lower shield 120 may be provided near the collimator 118 and inside the grounding adapter 104 or the upper sidewall 102. The lower shield 120 may include a tubular body 121 having a radially outwardly extending flange 122 disposed in the upper surface of the tubular body 121. The flange 122 provides a mating interface with the upper surface of the upper sidewall 102. The tubular body 121 of the lower shield 120 may include a shoulder region 123, the inner diameter of which is smaller than the inner diameter of the remainder of the tubular body 121. The inner surface of the tubular body 121 transitions radially inward along a tapered surface 124 to the inner surface of the shoulder region 123.

[0031] A shielding ring 126 may be disposed in the processing chamber 100, adjacent to the lower shielding member 120 and located between the lower shielding member 120 and the adapter plate 107. The shielding ring 126 may be at least partially disposed in a groove 128 formed by the opposite sides of the shoulder region 123 of the lower shielding member 120 and the inner sidewall of the adapter plate 107. The shielding ring 126 may include an axially projecting annular sidewall 127, the inner diameter of which is larger than the outer diameter of the shoulder region 123 of the lower shielding member 120.

[0032] A radial flange 130 extends from an annular sidewall 127. The radial flange 130 includes a protrusion 132 formed on its lower surface. The protrusion 132 may be a circular ridge extending from the surface of the radial flange 130 with an orientation substantially parallel to the inner diameter surface of the annular sidewall 127 of the shielding ring 126. The protrusion 132 is generally adapted to mate with a groove 134 formed in an edge ring 136 on the base plate support 108. The groove 134 may be a circular recess formed in the edge ring 136. The engagement of the protrusion 132 and the groove 134 centers the shielding ring 126 relative to the longitudinal axis of the base plate support 108. The base plate 101 (shown as supported on a lifting pin 140) is centered relative to the longitudinal axis of the base plate support 108 through coordinated positioning alignment between the base plate support 108 and the robot blade (not shown).

[0033] RF power source 180 can be coupled to processing chamber 100 via substrate support 108 to provide bias power between target 114 and substrate support 108. In some embodiments, a matching network (e.g., matching network 116) can be coupled between RF power source 180 and substrate support 108. RF power source 180 may have a frequency between about 400 Hz and about 60 MHz, such as about 13.56 MHz.

[0034] During operation, a robot blade (not shown) on which a substrate 101 is disposed extends through a substrate transfer port 109. A substrate support 108 can be lowered to allow transfer of the substrate 101 to a lifting pin 140 extending from the substrate support 108. The raising and lowering of the substrate support 108 and / or the lifting pin 140 can be controlled by a driver 142 coupled to the substrate support 108. The substrate 101 can be lowered onto a substrate receiving surface 144 of the substrate support 108. With the substrate 101 positioned on the substrate receiving surface 144 of the substrate support 108, sputtering deposition can be performed on the substrate 101. During processing, an edge ring 136 can be electrically insulated from the substrate 101.

[0035] After sputtering deposition, the substrate 101 can be raised to a position spaced apart from the substrate support 108 using the lifting pin 140. The raised position can be close to one or both of the shielding ring 126 and the reflective ring 148 adjacent to the adapter plate 107. The adapter plate 107 includes one or more lamps 150 coupled to the adapter plate 107 at a position between the lower surface of the reflector ring 148 and the concave surface 152 of the adapter plate 107. The lamps 150 provide light energy and / or radiant energy of visible or near-visible wavelengths, such as infrared (IR) and / or ultraviolet (UV) spectra. The energy from the lamps 150 is focused radially inward toward the back surface (i.e., the lower surface) of the substrate 101 to heat the substrate 101 and the material deposited on it.

[0036] After the substrate 101 is brought to a predetermined temperature, it is lowered onto the substrate receiving surface 144 of the substrate support 108. The substrate 101 can be rapidly cooled via conduction using the thermal control channel 146 in the substrate support 108. For example, a cooling device 153 can be connected to the substrate support 108 and configured to provide one or more coolants to the substrate support 108. The substrate 101 can be removed from the processing chamber 100 through the substrate transfer port 109 for further processing.

[0037] Controller 198 is coupled to processing chamber 100. Controller 198 includes a central processing unit 160, memory 158, and support circuitry 162. Controller 198 controls the process sequence to regulate the gas flow rate from gas source 110 into processing chamber 100 and to control the ion bombardment of target 114. Central processing unit 160 can be any form of general-purpose computer processor that can be used in an industrial environment. Software routines (e.g., instructions) can be stored in memory 158 (e.g., a non-transitory computer-readable storage medium), such as random access memory, read-only memory, floppy disk or hard disk drive, or other forms of digital storage device. Support circuitry 162 is conventionally coupled to central processing unit 160 and may include cache, clock circuitry, input / output subsystems, power supply, etc. When executed by central processing unit 160, the software routines transform the central processing unit into a dedicated computer controlling processing chamber 100, such that processes including the cooling process for substrate support 108 disclosed below are executed according to embodiments of this disclosure. The software routines can also be stored and / or executed by a second controller (not shown) located remotely from the processing chamber 100.

[0038] During processing, material is sputtered from target 114 and deposited onto the surface of substrate 101. Target 114 and substrate support 108 are biased relative to each other by power supply 117 or RF power source 180 to maintain plasma formed from process gas supplied by gas source 110. A DC pulsed bias power applied to collimator 118 also helps control the ratio of ions to neutral particles passing through collimator 118, thereby advantageously enhancing trench sidewall and bottom filling capabilities. Ions from the plasma are accelerated toward and impact target 114, causing target material to be expelled from target 114. The expelled target material and process gas form a layer with the desired composition on substrate 101.

[0039] Figure 2 It is configured for use with at least some embodiments of this disclosure. Figure 1A diagram of a magnet-to-target spacing system 200 used in conjunction with a processing chamber 100 is provided. For example, the magnet-to-target spacing system 200 includes a sensor 202 configured to provide a signal corresponding to the distance between the front face 204 of a magnet (e.g., one or more magnets 172) and the back face 206 of a target (e.g., target 114) while the magnet is rotated relative to the target. The sensor 202 can be any sensor capable of emitting and receiving beams. For example, in at least some embodiments, the sensor 202 is a laser sensor configured to emit a detection beam 208 toward the back face 206 of the target and receive a reflected beam 210 from the back face 206 of the target. The sensor 202 can be coupled to one or more regions of the magnet via one or more suitable coupling devices. For example, in the illustrated embodiment, the sensor 202 is coupled to a side surface of the magnet via one or more screws, nuts, bolts, etc.

[0040] The target spacing system 200 also includes a magnet controller 212 (e.g., controller 198), which is (wired or wirelessly) communicatively coupled to sensor 202 and configured to control the distance between the front side 204 of the magnet and the back side 206 of the target based on signals provided by sensor 202. For example, the magnet controller 212 is configured to determine the change in distance between the front side 204 of the magnet and the back side 206 of the target based on the travel speed of the detected beam 208, the time change from the emission of the detected beam 208 to the reception of the reflected beam 210, and a fixed scalar value (e.g., a fixed scalar value of 0.5). For example, the change in distance between the front side 204 of the magnet and the back side 206 of the target can be calculated using the following equation: Change in distance = 0.5 * Δt * V 射束 ..., (1) Where V 射束 = The travel speed of the detection beam 208, Δt = the time change from the emission of the detection beam 208 to the reception of the reflected beam 210, and 0.5 is a fixed scalar value. In at least some embodiments, the distance between the front side 24 of the magnet and the back side 206 of the target can vary from about 2.75 mm to about 3.25 mm during operation.

[0041] Figure 3 It is configured for use with at least some embodiments of this disclosure. Figure 1 A schematic diagram of the magnet-to-target spacing system 300 used in the processing chamber 100. Figure 3 The target spacing system 300 is basically similar to Figure 2The target spacing system 200. Therefore, this document only describes those features unique to the target spacing system 300. For example, as described above, the magnetron 170 may include one or more magnets 172, which may be coupled to the substrate 174. Therefore, the target spacing system 300 includes two or more magnets 172. Figure 3 (As shown in the diagram, two or more magnets are included), the two or more magnets comprising sensor 202 and magnet controller 212. Figure 3 In one embodiment, one of the two magnets is positioned adjacent to the center of the target 114 (above the center), and the other of the two magnets may be positioned adjacent to the peripheral edge of the target 114 (above the peripheral edge), which is typically where target bending occurs more frequently.

[0042] Figure 4 This is a flowchart of a method 400 for processing a substrate according to at least some embodiments of the present disclosure. For example, during PVD, a magnetron 170 may rotate one or more magnets 172 via an axis 176 to generate a magnetic field in the processing chamber 100 near the front of a target 114, thereby generating plasma, and thus a significant ion flux bombards the target 114, resulting in sputtering emission of the target material.

[0043] At 402, method 400 includes detecting the distance between the front face of the magnet and the back face of the target while rotating the magnet relative to the target. For example, at 402, while rotating one or more magnets 172, magnet controller 212 can detect the distance between the front face 204 of one or more magnets 172 and the back face 206 of the target 114. For example, sensor 202 can emit a detection beam 208 toward the back face 206 of the target 114. Next, magnet controller 212 can receive a reflected beam from the back face 206 of the target 114. Magnet controller 212 can detect whether the distance between the front face 204 of one or more magnets 172 and the back face 206 of the target has changed. For example, the change in distance between the front face 204 of one or more magnets 172 and the back face 206 of the target 114 is based on the travel speed of the detection beam 208, the time change from the emission of the detection beam 208 to the receipt of the reflected beam 210, and a fixed scalar value (e.g., the fixed scalar value could be 0.5). As described above, in at least some embodiments, the distance between the front side 204 of the magnet and the back side 206 of the target 114 can be calculated using equation (1).

[0044] Next, at 404, method 400 includes controlling the distance between the front face 204 of one or more magnets 172 and the back face 206 of the target 1147 to a desired value based on the detected distance. For example, when magnet controller 212 determines that the distance between the front face 204 of one or more magnets 172 and the back face 206 of the target 1147 has changed, magnet controller 212 may send a command signal to a magnet drive assembly (not shown) connected to the shaft 176 of the magnetron to move the shaft 176 up or down (e.g., to move the front face 204 of one or more magnets away from or closer to the back face 206 of the target 1147). For example, as Figure 3 As shown, when, for example, due to target bending (d1 less than d2), the distance between the front face 204 of one or more magnets 172 and the back face 206 of the target 114 has increased, the magnet controller 212 can send a command signal to the magnet drive assembly to move the axis 176 downward, for example, closer to the back face 206 of the target 114, in order to maintain a consistent distance (e.g., d3 = d1) between the front face 204 of one or more magnets 172 and the back face 206 of the target 114.

[0045] Although the foregoing are embodiments of this disclosure, other and further embodiments of this disclosure may be conceived without departing from the basic scope of this disclosure.

Claims

1. A magnet-to-target spacing system configured for use with an apparatus for processing a substrate, the magnet-to-target spacing system comprising: A sensor configured to provide a signal corresponding to the distance between the front side of the magnet and the back side of the target while rotating the magnet relative to the target, wherein the sensor is a laser sensor configured to emit a detection beam toward the back side of the target and receive a reflected beam from the back side of the target; as well as A magnet controller configured to control the distance between the front face of the magnet and the back face of the target based on signals provided by the sensor, wherein the variation of the distance between the front face of the magnet and the back face of the target is based on the travel speed of the detection beam, the time variation from the emission of the detection beam to the reception of the reflected beam, and a fixed scalar value. The change in distance between the front side of the magnet and the back side of the target is calculated using the following equation: Distance change = 0.5 Δt V 射束 , Where V 射束 =The travel speed of the detection beam and Δt =The time change from the time the detection beam is emitted to the time the reflected beam is received, and the fixed scalar value is 0.

5.

2. The magnet-to-target spacing system of claim 1, wherein the target is made of copper.

3. The magnet-to-target spacing system of claim 1, wherein the distance between the front side of the magnet and the back side of the target varies from 2.75 mm to 3.25 mm.

4. A processing chamber for processing a substrate, comprising: A substrate support member is disposed within the processing volume of the processing chamber and configured to support the substrate. The target is configured to sputter material toward the substrate support; A magnetron, the magnetron including a magnet that can rotate along a path during operation; A sensor configured to provide a signal corresponding to the distance between the front of the magnet and the back of the target while rotating the magnet relative to the target, wherein the sensor is a laser sensor configured to emit a detection beam toward the back of the target and receive a reflected beam from the back of the target; as well as A magnet controller configured to control the distance between the front face of the magnet and the back face of the target based on signals provided by the sensor, wherein the variation of the distance between the front face of the magnet and the back face of the target is based on the travel speed of the detection beam, the time variation from the emission of the detection beam to the reception of the reflected beam, and a fixed scalar value. The change in distance between the front side of the magnet and the back side of the target is calculated using the following equation: Distance change = 0.5 Δt V 射束 , Where V 射束 =The travel speed of the detection beam and Δt =The time change from the time the detection beam is emitted to the time the reflected beam is received, and the fixed scalar value is 0.

5.

5. The processing chamber of claim 4, wherein the target is made of copper.

6. The processing chamber of claim 4, wherein the distance between the front side of the magnet and the back side of the target varies from 2.75 mm to 3.25 mm.

7. A method for processing a substrate, comprising: While rotating a magnet relative to a target, the distance between the front face of the magnet and the back face of the target is detected, wherein detecting the distance between the front face of the magnet and the back face of the target includes: emitting a detection beam toward the back face of the target, and receiving a reflected beam from the back face of the target; and Based on the detected distance, the distance between the front side of the magnet and the back side of the target is controlled to a desired value, wherein the change in the distance between the front side of the magnet and the back side of the target is based on the travel speed of the detected beam, the time change from the emission of the detected beam to the reception of the reflected beam, and a fixed scalar value. The change in distance between the front side of the magnet and the back side of the target is calculated using the following equation: Distance change = 0.5 Δt V 射束 , Where V 射束 =The travel speed of the detection beam and Δt =The time change from the time the detection beam is emitted to the time the reflected beam is received, and the fixed scalar value is 0.

5.

8. The method of claim 7, wherein the target is made of copper.

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